The Fifth Congressional District, where seven Democratic and three Republican candidates are vying to succeed Edward J. Markey in the US House of Representatives, sweeps from the shore of Revere Beach to the storied brick buildings of Harvard Yard to the tony suburban streets of Weston and beyond to Framingham and Holliston.

But the geographic diversity of the district has not brought diversity in the Democratic candidates’ positions on the big political issues of the day.

In the party’s primary race in the heavily Democratic district, “progressive” is the word of choice for the rival candidates to describe their values. And their differences in policy are often ones of nuance.

The three Republicans are often opposite images of the Democrats on major issues. The winners of the two party primaries on Tuesday will face off in the Dec. 10 special election for the House seat left open by Markey’s election to the US Senate in June.

Among the Democrats, all of the candidates describe themselves as “prochoice,” or supporting abortion rights, and they all support expanding federal gun control measures, including more mandatory background checks on firearms purchases and bans on assault weapons and high- capacity magazines.

Most Democrats oppose the Supreme Court’s Citizens United decision, which allowed for unlimited spending on elections by corporations and labor unions. Most would vote for a US Senate-passed immigration reform bill, which would provide a path to citizenship for a large swath of the people in the United States illegally. And most see conservative Republicans in the US House as bearing primary responsibility for the federal government’s shutdown.

While the positions on many issues are strikingly similar among party colleagues, the candidates are not uniform in their views or backgrounds.

The seven Democrats range in age from 35 to 60; none live in the same community; five currently hold elective office; two are women.

Over the course of their campaigns, each has emphasized character traits and issues that might allow them to stand out in the minds of voters.

State Senator Will Brownsberger, who exudes a wonkish, intellectual persona at forums and debates, often notes he is someone who will take difficult positions if he believes them to be right, even if they aren’t popular or politically advantageous. The 56-year-old Belmont Democrat cites his view on the Citizens United case. Though he supports increased disclosure of now-secret political contributions, he said, his view that the ruling “was correctly decided’’ on First Amendment grounds is in stark contrast to Democratic Party orthodoxy.

One Brownsberger adviser recently called him “annoyingly principled,” a cheeky distillation of his message. “Who is really willing to do what’s right when it’s going to hurt them” politically, Brownsberger asked the audience at one event, and then supplied the answer: him.

State Representative Carl M. Sciortino, who married his longtime partner over the weekend, was first elected to the Legislature in 2004 after winning a close primary election that pivoted on his support for legal gay marriage. For this campaign, the 35-year-old Medford resident has positioned himself to the left of his opponents on domestic and foreign policy issues, and was early and vocal in his opposition to US military intervention in Syria.

In a recent TV ad, Sciortino calls himself “a Massachusetts liberal.” He stresses the point by using the definite article in italics in some of his literature: “The Progressive Democrat for Congress.” One issue he speaks about often is his cosponsoring a 2007 “buffer zone” law that bans people from protesting within 35 feet of the entrance, exit, or driveway of women’s health care clinics where abortions are performed.

State Senator Karen Spilka, the chamber’s majority whip, frames herself as a fighter who doesn’t back down from tough legislative skirmishes and gets results. “Since I’ve been in the State House, I’ve taken on the special interests that nobody else wanted to take on,” the 60-year-old Ashland resident said at one event. Her campaign often underlines her support from organized labor groups.

State Senator Katherine Clark, who has been endorsed by state Attorney General Martha Coakley and EMILY’s List, a national group that supports female candidates who favor abortion rights, has made women’s and family issues a centerpiece of her campaign. The 50-year-old from Melrose often derides “extremist” congressional Republicans in TV ads and at public forums. And she has made campaign stops — like one at a Head Start facility stung by federal funding cuts — to showcase the real-world effects of Capitol Hill actions.

Middlesex County Sheriff Peter J. Koutoujian, a 52-year-old former state representative from Waltham, emphasizes his positions and legislative successes on big policy issues, alongside work on less-noticed ones that, he says, still have an impact on people’s lives. Koutoujian, who also was a prosecutor in the Middlesex district attorney’s office, is particularly passionate about expanding measures to reduce gun violence, saying when it comes to “common sense gun control I’m willing to fight no matter who stands in the way or how long it takes.”

But on the campaign trail, he also mentions issues that don’t make national news. In forums and campaign videos, he cites
concerns he hears talking with voters and legislation he’s worked on regarding such issues as an antistalking law and a workplace smoking ban.

Martin Long, one of two Democratic candidates who don’t hold elective office, often notes he has written a book on congressional gridlock and how to end it. The 52-year-old Arlington Democrat also has played up what differentiates him from the crowded field.

“I am not a professional politician looking for promotion,” he said.

Stoneham resident Paul John Maisano, 59, who works in the construction industry, also has noted where he stands apart, calling himself “a candidate for the working person.”

At Democratic forums around the district, members of the Republican Party, not surprisingly, are often cast as boogeymen responsible for many of the nation’s problems. But the Democratic candidates have also indicated that they would look to work with the GOP, which controls the US House, on issues where interests aligned.

The Globe asked the Democratic candidates to name specific Republican members of Congress with whom they could work on an area of mutual concern. Clark, Koutoujian, Spilka, and Sciortino all named a GOP lawmaker they could work with. Brownsberger and Long did not.

While attention in this heavily Democratic district has focused on the Democratic candidates, the three GOP rivals are quietly battling for a spot on the general election ballot. They are actuary Tom Tierney of Framingham, Harvard nanophysics researcher Mike Stopa of Holliston, and businessman and lawyer Frank J. Addivinola Jr. of Boston.

All three Republicans oppose the Senate immigration bill and all support the Citizens United decision. Tierney and Addivinola describe themselves as “prolife,” and opposed to abortion rights, while Stopa says that he is personally opposed to abortion but that “Roe v. Wade is settled law.

“I believe that the right of a woman to have an abortion early in pregnancy should be protected,” he wrote in an e-mail that used a bold-face font to emphasize the word “early.’’

Whoever emerges as the GOP victor in next week’s primary will face a steep uphill battle on Dec. 10.The district voted for President Obama over former Massachusetts governor Mitt Romney by more than 30 percentage points last November, according to numbers compiled by the nonpartisan Cook Political Report. The results suggest the Democratic nominee would have an advantage.

But when he or she arrives on Capitol Hill as the most- junior member of the US House, the Fifth District representative will find that holding progressive political views would place them squarely in the minority.

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